Group III nitrides provide the important advantage of having a strong chemical bond which makes them highly stable and resistant to degradation under high electric current and intense light illumination conditions that are present at the active regions of optoelectronic devices. These materials are also resistant to dislocation formation once grown.
Due to the high growth temperatures of group III nitrides, there are presently only a limited number of known substrates suitable for supporting nitride film growth. The most commonly used substrate materials are sapphire and silicon carbide. These materials have significantly different lattice parameters and thermal expansion coefficients than the group III nitrides. Consequently, the interfaces formed between the substrates and nitrides lack coherence, resulting in increased interface strain and interface energy, and diminished film wetting. These factors largely affect the nitride film growth process and the quality of the resulting nitride films. For example, the growth process of group III nitrides on sapphire using known processes is highly three-dimensional. Group III nitride film growth occurs initially by the formation of discrete three-dimensional nitride islands on the substrate. These islands grow and coalesce with each other. Lattice matching is poor at the regions of the film at which the islands coalesce. High dislocation densities are generated at these regions. Dislocation arrays in the nitride film adversely affect the optoelectronic properties of devices fabricated on the nitride films by affecting carrier recombination processes in the active regions of the devices, and ultimately reducing emitted light intensities and device efficiencies.
Recently, many developers even seek new nitride platform with no immediate bulk GaN on the commercial horizon, and some engineers have started to look beyond silicon and SiC to composite materials and metals as a platform for nitride growth.
Of the many composite materials and metals as a candidate for new nitride platform, an increasing interest on TiN material has started to emerge. In general, a thin film of TiN has many purposes covering from mechanical hard-coating including military application, aerospace industry up to electronic, bio-material area due to outstanding chemical, mechanical, thermal stability. Though less visible, thin film TiN may also be used in the semiconductor industry. In copper-based chips, such films find use as a conductive barrier between a silicon device and the metal contacts used to operate it. While the film blocks diffusion of metal into the silicon, it is conductive enough (30-70 μΩ·cm) to allow a good electrical connection.
Nevertheless, little work to import transition metal nitride such as TiN-like material to be used for production of group III nitride compound semiconductor device has been conducted and to date, the growth method how to form TiN or co-deposit like a (Ti,Ga)N material on sapphire substrate with or without patterned shape for the purpose of optoelectronics application is not well established.